Fuel injection apparatus

ABSTRACT

A single solenoid coil controls the movement of a first and second armature respectively. Each armature is connected to a valve element for controlling a fuel supply and for controlling the delivery of the charge respectively. During the period of energization of the solenoid coil, both the first and second armatures are actuated, with the above noted valve elements being caused to open and closed in a predetermined sequence.

This invention relates to solenoid operated actuators and, inparticular, to solenoid operated fuel injection apparatus.

Fuel injection apparatus to inject fuel to a combustion chamber of anengine are well known. Equally well known are solenoid actuated fuelinjection apparatus.

For example, the applicant's U.S. Pat. No. 4,934,329 discloses a fuelinjection apparatus comprising a body with a port in the body providingcommunication with a combustion chamber of an engine in accordance withthe operation of a valve element connected to a stem extending through aport cavity in the body. Electromagnetic means within the body aredisposed about and operably connected to the valve stem. Accordingly,when the electromagnetic means is selectively energised andde-energised, the valve element may be moved to open and close the port.In that case, the electromagnetic means operates only the valve elementwhich opens and closes the port. Delivery of fuel to the port cavityoccurs in accordance with the control of a fuel metering unit, forexample, the unit marketed by the Rochester Products Division of GeneralMotors Corporation under the Trade Mark "Multec". Typically, the fuelmetering unit would ordinarily include a separate solenoid actuated fuelmetering valve.

U.S. Pat. No. 4,925,112, assigned to General Motors Corporation,discloses an injector adapted to deliver a charge of fuel and airdirectly into the combustion chamber of a two-stroke cycle engine. Apair of solenoid coils are aligned along a common axis situated betweenan armature that serves as a fuel metering valve and an armature thatoperates a charge delivery valve. The injector provides air and fuelinjectors integrated into a single package in an effort to minimise theoverall size of the injector.

The injectors described above are illustrations of units that, incertain applications, may present difficulties in respect to both sizeand cost. In the applicant's U.S. Pat. No. 4,934,329, the issue of theoverall size of the injector unit is illustrated. That is, there isdisclosed, in combination, a fuel metering unit and an individual fuelinjection apparatus. Such a combination may, in certain applications,suffer the disadvantage of bulkiness. In addition, the number of movingparts and the requirement for separate fuel metering and fuel injectionunits invariably implies a greater cost than may be the case with a unitin which the metering and injection units are integrated. It will alsobe understood that a multiplicity of solenoid actuated valves is itselfa cost factor.

U.S. Pat. No. 4,925,112, whilst disclosing the packaging of both ametering unit and an injection unit into the one apparatus, alsoillustrates the disadvantage of cost. In this patent, whilst there isdisclosed one overall injector unit, there are still two solenoid coilsactuating two valve armatures. The use of two individual coils createsthe disadvantage that the overall unit remains heavy and somewhat bulky.Further, a cost disadvantage may be encountered in respect of the costof two control channels and associated driver circuitry which arerequired for operation of the solenoid coils.

The above mentioned problems of size and cost are problems which becomemore difficult to ignore in price sensitive markets. Here, a costdifference of a small amount, in terms of a developed economy, may besignificant enough to render a product unmarketable whether or not theproduct is technically advantageous.

Single solenoid fuel injectors have been proposed previously. See, forexample, U.S. Pat. No. 5,004,162 and European Patent No. 404357.However, these systems have shown deficiencies when compared to systemswherein separate solenoids are provided for fuel and air chargedelivery. The use of a single solenoid in these systems has introducedlimitations in their operation. As the fuel and air charge valvearmatures are no longer independent, difficulties have arisen where anoverlap between fuel injection and air charge delivery is required, orwhere it is desired to commence fuel injection prior to commencing aircharge delivery.

It is a first object of the present invention to provide a solenoidactuated apparatus that addresses some of the disadvantages of size andcost identified above.

It is a second object of the present invention to provide a fuelinjection apparatus that addresses the some of the disadvantages of sizeand cost identified above.

With the first object in view, the present invention provides a solenoidoperated actuator including a single solenoid coil, a first armaturemovable in response to selective energising and de-energising of thesolenoid coil, a second armature movable in response to selectiveenergising and de-energising of the same solenoid coil, said firstarmature and second armature being respectively arranged to movesequentially as the single solenoid is de-energised.

More specifically there is provided a solenoid operated actuatorincluding a single solenoid coil and first and second armatures movablein response to selective energising and de-energising of the solenoid,said first and second armatures being respectively adapted to movesequentially in the same order between respective first and secondpositions as the single solenoid coil is energised and de-energised.

Preferably, the first and second armatures may be connected torespective first and second valves or switch elements and the armatures,whether actuating valves or switches or other means, may be designed tobe operated in any desired time relationship in respect to one another.Conveniently, the first armature may be operable to open and close thefirst valve when the solenoid coil is selectively energised andde-energised and the second armature may be operable to open and closethe second valve when the same solenoid coil is selectively energisedand de-energised. An electronic control unit may be employed to controlthe operation of the actuator through control of energisation of thesolenoid coil and may accordingly allow for separate or simultaneousoperation of the respective armatures, features that may be desired infuel injection applications as will be discussed hereinbelow. However,other modes of operation are also achievable.

The geometry of the armatures can be individually chosen to achieve orcontribute to the attaining of the desired respective operation of theactuators. Additionally, the valve elements may be appropriatelyindividually biased by springs or like devices into any desired extentand/or position. Typically, the valve or switch elements may be biasedinto a position corresponding with a closed position of the valve orswitch. The magnetic force generated by the energisation of the solenoidcoil to cause movement of the armature(s) is then required to overcomethe biasing force. In this sense, the extent of the biasing force actingon an armature itself can be calculated and imposed by an appropriatelyselected spring or like means, providing an additional design parameterto influence the control of the movement of the armature.

Similarly, the armatures may be positioned relative to each other or inrelation to the solenoid coil to achieve the desired performance. Theoperating parameters may be chosen for each application by way ofcalculation, trial and error or a combination of both.

Generally, a section of the armature, together with a solenoid housingor casing, forms a magnetic circuit around the solenoid coil. Themagnetic circuit provides the energy to actuate the armature, as thatpart of the armature which is in the magnetic circuit is acted on by themagnetic flux in the circuit. Primary and secondary magnetic circuitsare formed by the first and second armatures respectively in combinationwith the housing. It is desired to control the magnetic reluctance orresistance to magnetic flux in the respective magnetic circuitscorresponding to first and second armatures, to thereby control themagnetic force applied to the armatures.

Reluctance in the magnetic circuit can be controlled in a number ofways.

The gap between the armature and the pole face or working surface of thehousing, known as the magnetic gap, is one parameter on which reluctanceis dependent. As the size of the magnetic gap increases, the reluctanceof the magnetic circuit increases. It may be appreciated that eacharmature has at least two end positions, possibly corresponding with anopen or closed position of a valve or switch. The magnetic gap of eacharmature is generally at its largest at one end position and at itssmallest at the other end position. It is usual that in the at restposition the gap is at its largest and that when the armature is fullyactuated by operation of the solenoid, the gap is at its smallest. Assuch, there may be a substantial difference between the reluctance of aparticular magnetic circuit in the at rest and fully actuated positionsthereof.

End stops may be used to restrict the end positions and thus control themagnetic gaps associated with the respective armatures. Whereappropriate, low magnetic permeability spacers may be inserted betweenthe armature and the pole face to ensure that a minimum gap ismaintained.

The geometry of the armature itself affects the reluctance of themagnetic circuit. For example, reducing the cross-sectional area of thesection of the armature forming part of the magnetic circuit increasesthe reluctance of the circuit.

Selection of the material of which the armature is formed can alsoprovide a differential between the reluctance of the respective magneticcircuits.

The magnetic force applied to the armature acts against any biasingmeans holding the armature in its at rest position. Biasing means may bea spring or any other appropriate device.

It can be seen that by selecting appropriate magnetic gaps, armaturegeometry, armature material and biasing means for the first and secondarmatures, the solenoid energisation level required to actuate and holdthe respective armatures at desired positions can be predetermined inorder that the armatures are actuated in the sequence required.

The above enables manipulation of the magnetic characteristics of theprimary and secondary magnetic circuits, including the respectivearmatures, to provide the desired operation of the valve or switchelements. This in turn influences movement of the respective armaturesand provides a design parameter that can be selected to achieve thedesired performance of the first and second valve or switch elements. Inparticular, the geometry and area relationship of the respectiveattracting surfaces of each armature (i.e.: the surfaces that cometogether with a corresponding attracting surface of the ferro-magneticcasing to close the respective gaps) is an important design parameterthat may be engineered to achieve the desired operation of the first andsecond armatures.

The respective armatures may also be designed to be mechanicallyengaged. That is, the armatures may be designed such that one armaturemay cause by its movement, a desired movement of the second armatureunder mechanical influence. In this respect, the actuator allowsmovement of an armature by both mechanical and magnetic forces eitherthroughout the total or a part of the extent of movement of either ofthe armatures.

Of course, any one or more of these parameters may be selected to obtainthe desired operation of a solenoid actuated valve or switch apparatus.However, it will be understood that any of the parameters discussedabove can be varied in combination to achieve the desired operation ofthe apparatus.

With the second object in view, the present invention provides a fuelinjection apparatus comprising a solenoid coil; a first armatureconnected with a first valve element operable to open and close a fuelinlet valve to supply fuel to the fuel injection apparatus when thesolenoid coil is selectively energised and de-energised, and a secondarmature connected with a second valve element operable to open andclose a charge delivery valve to supply fuel from the injectionapparatus when the same solenoid coil is selectively energised andde-energised.

The operation of the second armature may control a flow of gas to theinjection apparatus wherein fuel is delivered entrained in a pressurisedgas, typically air, to a combustion chamber of an engine. However, thepresent invention is not limited to usage in a solenoid actuated fuelinjection apparatus in which such entrainment takes place.

In practice, the magnetic force generated by the solenoid coil will beacting predominantly against predetermined biasing forces, generated bysprings or like means used to bias the armatures into a preferredposition, generally according with a closed position of the valves. Byexerting sufficient magnetic force on the appropriate armature, byappropriate control over the supply of current to the solenoid coil, thefuel inlet valve can be operated to allow a metered quantity of fuelinto the fuel injection apparatus. This metered quantity of fuel canoptionally be admixed with a pressurised gas such as air.

The electrical current to energise the solenoid coil may then preferablybe increased at the required rate to open the second charge deliveryvalve to deliver the gas-fuel charge to a combustion chamber of anengine. Depending upon the configuration of the armatures of the fuelinjection apparatus, and the design of the magnetic circuits for controlthereof, the fuel inlet valve may remain open during all, or a portion,of the open time of the charge delivery valve or can in fact close as orbefore the charge delivery valve opens. In this respect, it will beunderstood that such overlapping operation of the charge delivery andfuel inlet valves is an inherent feature of the fuel injection apparatusdescribed herein.

Such overlap of the operation of the charge delivery and fuel inletvalves may be relied upon, for example, to provide fuel fluxing controlas described in the applicant's U.S. Pat. No. 4,800,862, the contents ofwhich are hereby incorporated by reference. In such a case, the geometryand/or reluctance of the primary and secondary magnetic circuitsrelating to the first and second armatures influenced, for example, bythe dimensions and geometry of the respective armature gaps, can also bevaried by trial and error and/or calculation to achieve the desiredoverlapping operation of the valve elements.

It may typically be expected that the operation of the fuel inlet and/orcharge delivery valves will require energisation of the solenoid coil intimed relation to the engine operating cycle to achieve the desiredengine performance.

Further, it should be understood that the present invention is notlimited in application to a specific fuel injector type. The presentinvention is therefore equally applicable to injectors in which fuel isdelivered through a hollow stem connected to the charge delivery element(as in the manner disclosed in the applicant's U.S. Pat. No. 4,934,329,the contents of which are hereby incorporated by reference) and toinjectors in which fuel or fuel/gas mixtures pass through or into anannular cavity surrounding the stem of the charge delivery valveelement.

In the context of fuel injection apparatus, the actuator controlling thefuel metering and the fuel delivery (injection) as now proposed can havea number of advantages as follows:

(a) A separate solenoid operated fuel metering valve may be avoidedthrough avoidance of a separate bulky fuel metering unit. Accordingly,the size of the combined fuel metering/injection unit may be reduced.

(b) By integration of the fuel metering and injection units, it can bepossible to reduce the mass of moving components, particularly thearmatures, with benefits in terms of lesser noise, vibration andharshness.

(c) The use of a single solenoid coil can reduce the overall powerrequirement of the fuel injection apparatus.

The present invention will be better understood from the followingdescription of one embodiment thereof made with reference to theaccompanying drawings in which:

FIG. 1 is a sectional view of a fuel injection apparatus actuated by asolenoid operated valve actuator; and

FIG. 2 is a magnified view of region A of FIG. 1, showing in more detailthe construction of that region.

FIG. 3 is a series of plots illustrating the performance of the injectoras the current applied to the solenoid rises and falls during one cycle.

Referring now to FIG. 1, there is shown a fuel injector 1 having aferro-magnetic housing 2 in which there is provided a single solenoidcoil 3. A fuel inlet 4 connectable to a supply of pressurised fuel, anda gas inlet 5 connectable to a supply of pressurised gas, are alsoprovided in the housing 2. Ordinarily, the pressurised gas will beemployed to propel quantities of fuel, entering the fuel injector 1through fuel inlet 4, into the combustion chamber (not shown) of aninternal combustion engine. Conveniently, in such a case, the gas is airand the source of pressurised air is an air compressor (not shown)driven in dependence on the operation of the engine.

In injector 1, fuel and air are admixed in chamber 6 and enter throughbores 7 into a fuel chamber 10 to travel through passage 20, formed in astem 24 extending from a valve element 21 which is selectively operableto open and close the charge delivery port 22. For this purpose,apertures are formed in the region 23 of the stem 24.

The fuel inlet 4 is itself selectively operable to bring the injector 1into communication with the fuel supplied through fuel inlet valve 8,which is opened and closed in timed relation to a cycle of the engine.To this end, fuel inlet valve 8 is rigidly connected to a fuel inletarmature 9 and is biased into a closed position, by a spring 11 ofappropriately selected physical characteristic, whereby the fuel inletarmature 9 is axially spaced from the inner wall 126 of the solenoid todefine an axial air gap or magnetic circuit gap at 12.

Similarly, the charge delivery valve stem 24 is rigidly connected to acharge delivery armature 26 and is also biased into a closed position bya spring 27 of appropriately selected physical characteristic. Thecharge delivery armature 26 thereby define the axial air gap or magneticcircuit gap 28 between the armature 26 and the inner wall 126 of thesolenoid.

Turning now to FIG. 2, pole face 30 of internal housing member 32 isshown adjacent armatures 9, 26. A low magnetic permeability spacer 34 ispositioned between armature 9 and pole face 30. Due to the lowpermeability of the spacer 34, the effective magnetic gap 12 is stillmeasured between the lower face 36 of the armature 9 and the pole face30. Although the spacer 36 does not affect the magnetic gap 12, itprovides a physical barrier preventing the armature 9 from moving withina physical distance of the pole face 30 by at least the axial dimensionof the spacer 35. This sets the minimum value of the magnetic gap 12. Incontrast, the armature 26 is able to approach the pole face 30 and theminimum dimension for the magnetic gap 28 is effectively zero. Therespective minimum magnetic gap for each armature 9, 26 occurs when thearmature 9, 26 is in the fully actuated state.

The maximum dimension for the magnetic gaps 12, 28 is set by end stopsin the form of engagement of the valves 8, 21 with their respectiveseating surfaces. Thus the magnetic gaps 12, 28 vary from minimum(associated with valves 8, 21 respectively being in the open condition)to maximum (associated with valve 8, 21 respectively being in the closedcondition).

The maximum dimension of the magnetic gap 28 of the air charge deliveryarmature 26 is selected to have a greater axial dimension than themaximum magnetic gap 12 of the fuel inlet armature 9.

The armature 9 forms part o the primary magnetic circuit and thearmature 26 forms part of the secondary magnetic circuit.

Movement of charge delivery armature 26 must be caused by a magneticforce equal to or greater than the biasing spring force imposed byspring 27. Similarly, the movement of fuel inlet armature 9 must becaused by a magnetic force equal to or greater than the biasing springforce imposed by spring 11. In this embodiment, spring 27 imposes aslightly greater biasing force on armature 26 than spring 11 imposes onarmature 9.

As a result of the differential between forces imposed by the respectivesprings 11, 27 and between maximum magnetic gaps of the respectivearmatures 9, 26, when the solenoid 3 is energised to a predeterminedlevel of current, there will be a tendency for the fuel inlet valve 8 toopen, with the charge delivery valve element 21 opening only on furtherincreases in the level of current. This is desirable to achieve adesired fuel fluxing and emissions performance as described in theapplicant's U.S. Pat. No. 4,800,862, the contents of which are herebyincorporated by reference.

The operation of fuel injector 1 will now be described, with appropriatereference to FIGS. 1 and 2 as follows.

Energisation of solenoid coil 3 by increasing the current suppliedthereto causes a rise of the attracting magnetic force acting on botharmatures 9 and 26. As is known to those skilled in the art, anattracting force exists across each respective gap 12 and 28 and servesto ultimately attract each respective armature 9 and 26 towards poleface 30 which, together with a portion of the ferro-magnetic housing 2and internal housing 32, serves to complete a respective magnetic fluxpath, which includes the respective armatures 9 and 26. The springpre-load of spring 11 is set such that shortly before magneticsaturation of the armature gap 12 occurs, the magnetic force acting onthe fuel inlet armature 9 is sufficient to overcome the spring forceimposed by spring 11 and gap 12 commences to approach its minimumdimension.

As discussed above, the primary magnetic circuit is designed such thatwhen the armature gap 12 is at its minimum value, "zero" reluctancebetween the respective surfaces is avoided. At this point, theattracting magnetic force acting on the charge delivery armature 26 isstill not sufficient to overcome the spring pre-load imposed by spring27, hence charge delivery port 22 remains closed. This first stepequates to the opening of a separate fuel metering nozzle in a prior arttwo fluid fuel injection system to enable fuel to flow into a holdingchamber of a charge delivery injector. In the present case, fuel isenabled to enter the fuel chamber 10 via the fuel inlet 4.

Further increase in the current energising solenoid coil 3 causes noappreciable increase in the holding force acting on fuel inlet armature9 as the circuit is effectively saturated, but the magnetic force actingon the charge delivery armature 26 continues to rise. At this point, thesecondary magnetic circuit becomes fully saturated. Since the forceinduced by the energising current, is sufficient to overcome the setbiasing pre-load of the spring 27, the charge delivery armature 26commences to close the gap 28. The reduction in size of the armature gap28 does not cause further appreciable increase of the magnetic flux asthe secondary magnetic circuit is saturated. Hence, the magnetic forcesacting on both armatures 9 and 28 remain effectively unchanged, but bothvalves are open and hence there is an overlap between the opening of thecharge delivery port 22 and of the fuel inlet valve 8.

As both magnetic gaps 12, 28 are at their minimum, the reluctance ofboth primary and secondary magnetic circuits is decreased, and adecrease in current is possible without affecting the opened conditionof the valves 8 and 21. This is accordingly implemented to reduce thecurrent in the solenoid which reduces the power consumption of thesystem. This "holding current", as it is commonly known, whilst beingless than the currents necessary to open the valves 8 and 21, issufficient to maintain the valves 8 and 21 in the opened positions.

In respect of a prior art two fluid injection system, the next steprelates to a separate fuel metering injector continuing to meter fuel toa charge delivery injector while the charge delivery injector isinjecting the existing fuel air mixture into the combustion chamber ofan engine. In the present case, fuel entrained in air has commencedbeing delivered or injected directly into the combustion chamber of theengine whilst a certain amount of fuel is still being metered into thefuel chamber 10 via the fuel inlet 4. Hence, depending on the openingrelationship of the fuel inlet valve 8 and the charge delivery valveelement 21, a desired degree of fuel fluxing may be achieved aspreviously described with reference to injector systems whereinindividual solenoids are used to control fuel metering and fueldelivery.

Further reduction of the current in the example now described to apredetermined level reduces the magnetic flux in the magnetic circuit toa point where it is no longer sufficient to overcome the biasing springpre-load of the spring 11. At this point, the armature gap 12 will beginto open and hence the fuel inlet valve 8 commences to close. Theincreased reluctance of the primary circuit caused by the inclusion ofthe low permeability spacer 36 (providing a non-zero minimum magneticgap 12) encourages the opening of the magnetic gap 12 prior to themagnetic armature 26. This is because magnetic flux of the solenoid coil3 will tend to flow through the second magnetic circuit due to lowerreluctance, thus providing energy to hold the air charge armature 26 incontact with the pole face 30.

If the solenoid current is held steady, the charge delivery valveelement 21 may be maintained open whilst the fuel inlet valve 8 isclosed. This third step equates to the fuel metering injector of a priorart two injector, two solenoid system being closed and the chargedelivery injector thereof being open to deliver some or all of theremaining metered quantity of fuel. Further, this may also equate to thesituation where all of the metered quantity of fuel has been deliveredand due to certain desired operating strategies, it is necessary tomaintain the charge delivery injector open. For example, this may bedesirable for certain periods of engine operation to allow a cleanroutine strategy as described in the applicant's U.S. Pat. No. 5,195,482which is incorporated herein by reference.

Finally, switching off or reducing the current energising the solenoidcoil 3 to zero will cause the armature gap 28 to open and hence closethe charge delivery port 22.

Referring now to FIG. 3 of the drawings which consist of a graph whereinthere is plotted the gap between the respective armatures and thesolenoid as the current in the solenoid rises and falls through onecycle. In addition, there is also plotted the force applied to thearmature as the current in the solenoid passes through its cycle.

Plot B is the current variation in the solenoid as it rises at a steadyrate from zero to a maximum and then decays at a steady rate to zeroagain. As the current in the solenoid increases, the magnetic forceapplied to the respective armatures 9 and 26 increases. However, due tothe construction of the device, and in particular as the gap between thepole face 30 and armature 9 is less than that between the pole face 30and armature 26, the magnetic force applied to armature 9 as indicatedby Plot C rises more rapidly than that applied to armature 26 asindicated in Plot D.

As a result of this more rapid rise in the magnetic force C, thearmature 9 will be the first to commence to move in the directiontowards the solenoid, this movement commencing at point E1 in Plot E ofthe position of armature 9. Shortly after the armature 9 has travelledthe full extent possible, as defined by the contact thereof withabutment points in the fuel injector 1, the armature 9 becomessaturated, the force applied to the armature 9 will remain substantiallyconstant although the current continues to rise. At this condition thevalve B has moved to the fully open position.

Considering now the operation of armature 26, it will be noted thatmovement thereof does not commence until a significant period after theapplication of the current to the solenoid and after the armature 9 hasreached its full extent of movement. The point of commencement ofmovement of the armature 26 is indicated at F1 in Plot F of the positionof the armature 26. It is thus seen that the armature 9 will move to itsfull extent as indicated by Plot E, a considerable time before thearmature 26 has reached its full open position as represented by Plot F.

Upon the current commencing to reduce as indicated at G, the magneticforce applied by the solenoid to the respective armatures 9 and 26 willcommence to decay, but the armature 9 leaves its magnetically saturatedcondition prior to armature 26 doing so, and once the armature 9 is nolonger magnetically saturated further reduction in current leads to amore rapid decrease in the magnetic force applied to the armature 9, andhence the armature 9 will commence to move away from the solenoid underthe action of the spring 11 as indicated at E2 earlier than when thearmature 26 commences to move away from the solenoid as indicated at F2.Hence the valve 8 connected to the armature 9 will close prior to thevalve 21 connected to the armature 26.

It is thus seen that the relative timing of the opening and closing ofthe valves can be controlled and adjusted by appropriate control ofcurrent flowing in the solenoid and the rate and timing of the change ofthat current.

Referring now to FIG. 3 of the drawings which consist of a graph whereinthere is plotted the gap between the respective armatures and thesolenoid as the current in the solenoid rises and falls through onecycle. In addition, there is also plotted the force applied to thearmature as the current in the solenoid passes through its cycle.

Plot B is the current variation in the solenoid as it rises at a steadyrate from zero to a maximum and then decays at a steady rate to zeroagain. As the current in the solenoid increases, the magnetic forceapplied to the respective armatures 9 and 26 increases. However, due tothe construction of the device, and in particular as the gap between thepole face 30 and armature 9 is less than that between the pole face 30and armature 26, the magnetic force applied to armature 9 as indicatedby Plot C rises more rapidly than that applied to armature 26 asindicated in Plot D.

As a result of this more rapid rise in the magnetic force C, thearmature 9 will be the first to commence to move in the directiontowards the solenoid, this movement commencing at point E1 in Plot E ofthe position of armature 9. Shortly after the armature 9 has travelledthe full extent possible, as defined by the contact thereof withabutment points in the fuel injector 1, the armature 9 becomessaturated, the force applied to the armature 9 will remain substantiallyconstant although the current continues to rise. At this condition thevalve B has moved to the fully open position.

Considering now the operation of armature 26, it will be noted thatmovement thereof does not commence until a significant period after theapplication of the current to the solenoid and after the armature 9 hasreached its full extent of movement.

The point of commencement of movement of the armature 26 is indicated atF1 in Plot F of the position of the armature 26. It is thus seen thatthe armature 9 will move to its full extent as indicated by Plot E, aconsiderable time before the armature 26 has reached its full openposition as represented by Plot F.

Upon the current commencing to reduce as indicated at G, the magneticforce applied by the solenoid to the respective armatures 9 and 26 willcommence to decay, but the armature 9 leaves its magnetically saturatedcondition prior to armature 26 doing so, and once the armature 9 is nolonger magnetically saturated further reduction in current leads to amore rapid decrease in the magnetic force applied to the armature 9, andhence the armature 9 will commence to move away from the solenoid underthe action of the spring 11 as indicated at E2 earlier than when thearmature 26 commences to move away from the solenoid as indicated at F2.Hence the valve 8 connected to the armature 9 will close prior to thevalve 21 connected to the armature 26.

It is thus seen that the relative timing of the opening and closing ofthe valves can be controlled and adjusted by appropriate control ofcurrent flowing in the solenoid and the rate and timing of the change ofthat current.

Of course, the above described sequence of events is ideally to becarefully controlled in relation to the point in an engine cycle wherethe respective valves 8 and 21 are required to be opened or closed.Thus, the timing of changes in current is advantageously set by anelectronic control unit (ECU) which controls total operation of the fuelinjector 1. Such appropriate timings are the subject of discussion inthe applicant's U.S. Pat. No. 4,800,862 and references may be made tothat disclosure.

It is to be understood that the actuator as disclosed herein is not tobe limited in its application to a fuel injector as above described. Itmay be well understood that the actuator is equally applicable to othertypes of fluid injectors without departing from the present invention.

Further, it is to be understood that whilst the present embodiment hasbeen described with respect to a magnetic circuit comprising highreluctance elements such as air gaps in a parallel configuration, otherconfigurations of such elements, such as serial configurations, may beenvisaged.

The primary or fuel inlet armature 9 and secondary or charge deliveryarmature 26 may be mechanically engaged in some manner. Referring to theabove description it will be noted that closure of the fuel inletarmature gap 12 did not cause any mechanical influence over the armature26. However, the system may be designed by use of suitable mechanicallinkage, arrangement of biasing springs or arrangement of the armatures9 and 26 such that the opening of the armature gap 12 tends to cause theopening of armature gap 28 or such that the opening of armature gap 28tends to cause the closing of armature gap 12. It may be wellappreciated that the reluctance of both gaps may also be chosen, perhapsin conjunction with selection of spring pre-load forces, to achieve asimilar result.

For specific operations or purposes, it may be desirable to prevent thearmature 9 from being actuated. In this regard, physical means may beprovided to axially rotate the armature 9 into a position which wouldprevent movement thereby. Accordingly, it would then be possible toactuate only the armature 26 to open the charge delivery port 22. Thismay be desirable to enable the use of various control strategies duringcertain periods of engine operation. Such control strategies may includethe clean routine strategy as described hereinbefore and a gas volumepump-up strategy as disclosed in the applicant's U.S. Pat. No. 4,936,279which is hereby incorporated by reference.

It will be understood that the actuator disclosed herein is not limitedto fuel injection applications and may be applied in other fieldswithout departing from the scope of the present invention.

We claim:
 1. A fuel injection apparatus comprising a single solenoidcoil, a first armature connected with a first valve element operable toopen and close a fuel inlet valve to supply fuel to a fuel injectionchamber when the solenoid coil is selectively energized andde-energized, and a second armature connected with a second valveelement operable to open and close a charge delivery valve to supplyfuel from the injection chamber when the same solenoid coil isselectively energized and de-energized, wherein said first valve elementand said second valve element can be opened and closed in the same orderas the single solenoid coil is energized and de-energized.
 2. A fuelinjection apparatus as claimed in claim 1, wherein said apparatus isoperable to open or close the first valve element prior to the openingand closing respectively of said second valve element.
 3. A fuelinjection apparatus claimed in claim 1 or 2 wherein said second armaturecontrols air charge flow in the apparatus in which fuel is entrained inan air charge to delivery to an internal combustion engine.
 4. A fuelinjection apparatus comprising:a single solenoid coil; a first armatureconnected with a first valve element operable to open and close a fuelinlet valve to supply fuel to a fuel injection chamber, and a secondarmature connected with a second valve element operable to open andclose a charge delivery valve to supply fuel from the injection chamber,the first armature being movable between first and second configurationsin response to selective energization of the solenoid coil, the secondarmature being movable between first and second configurations inresponse to selective energization of the solenoid coil, said firstconfiguration of each armature corresponding to a closed configurationof the respective valve and said second configuration of each armaturecorresponding to an open configuration of the respective valve;wherein(i) energization of the solenoid coil first causes said firstarmature to move from its first configuration to its secondconfiguration, (ii) further energization of the solenoid coil causessaid second armature to move from its first configuration to its secondconfiguration, and (iii) when both armatures are in their respectivesecond configurations, reduction in energization level of the solenoidcoil to a first predetermined level will result in the return of thefirst armature to its first configuration, and subsequent reduction inthe energization level of the solenoid coil to a second predeterminedenergization level lower than said first predetermined energizationlevel, will result in the return of the second armature to its firstconfiguration.
 5. A fuel injection apparatus as claimed in claim 4,wherein said first configuration of each respective armature correspondsto an at rest configuration of each said armature, and said secondconfiguration of each respective armature corresponds to an actuatedconfiguration of said armature.
 6. A fuel injection apparatus as claimedin claim 4, wherein the movement of the first and second armatures arerespectively controlled by a magnetic armature gap provided between eachsaid armature and a pole face of the apparatus.
 7. A fuel injectionapparatus according to claim 6, wherein a physical abutment is providedto control the magnitude of the magnetic armature gap in relation to therespective armature.
 8. A fuel injection apparatus according to claim 7,wherein the physical abutment is a spacer of low magnetic permeabilitypositioned between a pole face of the solenoid operated actuator and anopposing surface of said respective armature.
 9. A fuel injectionapparatus according to claim 6, wherein the movement of the first andsecond armatures are further controlled by a bias means providing a biasagainst at least one of the armatures when the solenoid coil actuatesthe respective armature.
 10. A fuel injection apparatus according toclaim 9, wherein the bias means is a spring acting against the forceproduced by the energization of the solenoid coil.
 11. A fuel injectionapparatus comprising:a single solenoid coil; a first armature connectedwith a first valve element operable to open and close a fuel inlet valveto supply fuel to a fuel injection chamber, and a second armatureconnected with a second valve element operable to open and close acharge delivery valve to supply fuel from the injection chamber, thefirst armature being movable between first and second configurations inresponse to selective energization of the solenoid coil, the firstarmature being biased towards said first configuration by a firstbiasing element, the second armature being movable between first andsecond configurations in response to selective energization of thesolenoid coil, the second armature being biased towards said firstconfiguration by a second biasing element, said first configuration ofeach armature corresponding to a closed configuration of the respectivevalve and said second configuration of each armature corresponding to anopen configuration of the respective valve, the first armature beingactuated towards its second configuration at a first predeterminedsolenoid energization level, the second armature being actuated towardsits second configuration at a second predetermined solenoid energizationlevel, higher than said first solenoid energization level; wherein whenboth first and second armatures are in their respective secondconfigurations, at a given solenoid energization level, the magneticforce above the biasing force in the second armature is stronger thanthe magnetic force above the biasing force in the first armature, suchthat the first armature returns to its first configuration at a solenoidenergization level higher than the solenoid energization level at whichthe second armature returns to its first configuration.
 12. A fuelinjection apparatus claimed in claim 11, wherein said second armaturecontrols air charge flow in the apparatus in which fuel is entrained inan air charge to deliver to an internal combustion engine.
 13. A methodof operating a fuel injection apparatus comprising a single solenoidcoil, a first armature connected with a first valve element operable toopen and close a fuel inlet valve to supply fuel to the fuel injectionapparatus, and a second armature connected with a second armatureconnected with a second valve element operable to open and close acharge delivery valve to supply fuel from the fuel injection apparatus,the first armature being movable between first and second configurationsin response to selective energization of the solenoid coil, said firstconfiguration of each armature corresponding to a closed configurationof the respective valve and said second configuration of each armaturecorresponding to an open configuration of the respective valve; themethod comprising(i) energizing the solenoid coil to a firstenergization level to cause said first armature to move from its firstconfiguration to its second configuration, (ii) further energizing ofthe solenoid coil to a second energization level higher than the firstenergization level to cause said second armature to move from its firstconfiguration to its second configuration, and (iii) when both armaturesare in their respective second configurations, reducing the energizationlevel of the solenoid coil to a first predetermined energization levelto thereby return the first armature to its first configuration, andsubsequently further reducing the energization level of the solenoidcoil to the second predetermined energization level to thereby returnthe second armature to its first configuration.
 14. A method ofoperating a fuel injection apparatus comprising a single solenoid coil,a first armature connected with a first valve element operable to openand close a fuel inlet valve to supply fuel to the fuel injectionapparatus, and a second armature connected with a second valve elementoperable to open and close a charge delivery valve to supply fuel fromthe fuel injection apparatus, the first armature being movable inresponse to selective energization of the solenoid coil, the secondarmature being movable in response to the said selective energization ofthe solenoid coil; the method comprising energizing the solenoid coilfrom zero to a predetermined level and subsequently returned to zerosuch that the movement of the first and second armatures provide thefollowing valve sequence:(i) both fuel inlet valve and charge deliveryvalve are closed (ii) fuel inlet valve opens, charge delivery valveremains closed (iii) fuel inlet valve remains open, charge deliveryvalve opens (iv) fuel inlet valve remains closed, charge delivery valvecloses.